The present invention relates to a system mounted on a vehicle to provide in sequence navigation information for primary routes between given starting and destination locations. More particularly, the present invention relates to a vehicle navigation system that displays primary and secondary route information in a quick and convenient way that facilitates vehicle movement between given starting and destination locations.
Vehicle-mounted navigation systems that compute an optimal route from a starting point to a destination and guide the vehicle along the route are known in the prior art. A conventional navigation system provides primary route information to a driver with reference to an approaching intersection. The information shows what direction the vehicle should take, at the approaching intersection, to follow the optimal route to the given destination. Typically, a navigation system predetermines directional symbol's that represent the possible directions of advancement for any given intersection. In use the navigation system displays the symbol that best illustrates the primary route information.
This type of navigation system can cause problems if the angle between roads at an intersection is small. In that case primary route information from the navigational system may not adequately inform the driver which road to enter at the intersection.
A navigational system to overcome this problem is disclosed in Japanese Laid-Open Patent Application No. 61-190698. The system described therein computes the angle between intersecting roads. The roads are then graphically displayed to the vehicle driver at the correct angle, with a symbol showing the direction of vehicle travel superimposed upon the display. With this arrangement, the driver can dearly determine which road to enter. Unfortunately, however, the computational burden to produce the graphical information for this display is substantial, making the processing time excessively long.
Another navigation system of the graphical type is disclosed in Japanese Laid-Open Patent Application No. 62-93617. The system described therein displays a plurality of arrows that correspond to the directions of the roads that the vehicle can enter at the next intersection. The one arrow that corresponds to the direction of the road the vehicle should enter is displayed in color. Unfortunately, drivers using this navigation system can not easily pick out the images of the roads from the plurality of superimposed arrows.
Thus neither of these prior-art systems is satisfactory, and there is room for improvement in vehicle navigation systems with graphical displays.